For the purpose of improving surface properties of molded parts made of metals or plastics, cured coatings of organosilicon compounds are often formed on the surface of molded parts, as is well known in the art. This approach, however, suffers from a problem of very poor adhesion between metals and organosilicon compounds except for the combinations of certain metals with organosilicon compounds having a limited chemical structure.
There remained a demand for adhesion promoters and primer compositions capable of improving the adhesion between them. Exemplary compositions include a primer composition based on a polyalkylene imine and an epoxy bond-containing trialkoxysilane as disclosed in JP-B 54-28430; a composition comprising a compound obtained by ester exchange of a polyester or polyether polyol with an alkoxysilane and a polyisocyanate as disclosed in JP-B 48-41697; a methyl methacrylate based composition as disclosed in JP-A 52-138565; a primer composition based on an epoxyalkyltrialkoxysilane as disclosed in JP-A 54-81378; a primer composition comprising a certain silane and an acid anhydride as disclosed in JP-A 54-155229 corresponding to U.S. Pat. No. 4,246,038; and a composition comprising a co-hydrolysate of two or more silanes and a methylol melamine alkyl ether as disclosed in JP-A 55-99930.
Unfortunately, all these compositions fail to impart fully satisfactory adhesion, hot water resistance and heat resistance to objects.
It is a common practice to encapsulate semiconductor members such as transistors, diodes, ICs and LSIs with resin materials such as epoxy resins. The encapsulation of semiconductor members with resin materials often causes the semiconductor members to be degraded by water and ionic impurities that migrate thereto from the resin materials. In one proposed solution to this problem, a semiconductor member is coated with a polyimide resin having good heat resistance, electrical properties and mechanical properties for protection, prior to the encapsulation with a resin material. In general, the polyimide resin can impart excellent properties like heat resistance to the objects. Since the polyimide resin is insoluble in solvents other than some high-boiling organic solvents, it is a common practice that the polyimide resin in a polyamic acid state as a precursor thereof is dissolved in an organic solvent, and the solution is coated onto a semiconductor member, followed by heat curing (for imidization) to form a cured coating.
In forming the polyimide resin coating by this method, however, the heat treatment for converting polyamic acid to polyimide requires a high temperature of at least 300° C. and a long time. The high temperature, long term heating involved in this method is disadvantageous from the process aspect and from the standpoint of energy saving. On the other hand, insufficient heating will allow the polyamic acid to be left in the structure of the resulting resin. The residual polyamic acid can cause to decline the moisture resistance, corrosion resistance and other properties of the polyimide resin. In particular, when the resin material is used as an insulating protective coating on semiconductor members, such decline of resin properties can cause degradation and short life to the semiconductor members, raising a serious problem. It is desired to overcome these problems.
In the current semiconductor art, packages become smaller in both size and thickness, and the surface mount technology becomes the mainstream of the component-on-substrate mounting technology. Under the circumstances, prior art epoxy resin compositions become short to maintain reliability. In addition, solders have lately been replaced by lead-free solders, which raises the solder reflow temperature up to 260° C. If packages are subjected to soldering after moisture absorption, cracks can occur in the packages or even in the absence of cracks, a substantial loss of moisture resistance can take place. From this standpoint too, there remains a need for a heat resistant primer composition of quality.
JP-A 5-009254 and JP-A 6-116517 disclose siloxane-modified polyamide-imide resins. These resins have insufficient bond strength to copper foil and still suffer from the problems including lower glass transition temperature (Tg) and degraded heat resistance of cured film.